(1) Field of the Invention
The present invention relates generally to improvements in broadcast towers, and in particular to modifications improving the use of such towers for the co-location of wireless antennas for use with cellular telephones, and other telecommunications devices.
(2) Description of the Prior Art
Conventional radio broadcast towers, e.g., AM broadcast towers, are not commonly used as supports for co-locating wireless antennas used for cellular telephone and other telecommunication uses. While convenient, these towers have several disadvantages.
In typical standalone AM operations, the base of the tower is fenced and personnel rarely come near the base area of the tower where high voltages may exist on accessible elements of the antenna system within the fence. When access occurs, it is usually by trained engineers. When tower space is rented to wireless users, however, the tower base area must be accessed by a variety of individuals who may not be aware of the dangerous voltages that may exist in their vicinity.
An additional complication of co-location use is that lessees must frequently climb the tower to inspect, install or adjust attached antennas. The relatively small wires required by conventional antennas towers, such as the folded unipole antenna manufactured by the LBA Technology, Inc., Greenville, N.C., are prone to tangle with tools and other equipment carried by the climbers, creating an unsafe condition. This hazard is of particular concern at the bottom of the tower when the climber is getting onto or off of the tower.
The present invention relates to a network of insulation features added to an antenna such as the folded unipole type to protect workers near or on the base area of the tower. The folder unipole consists of one or more vertical wires emanating from insulator/tension assemblies spaced around the tower and typically a few feet off the ground. If there are multiple wires, they are typically connected by an encircling horizontal wire xe2x80x9cbase ringxe2x80x9d. An additional wire is attached from the base ring to an antenna tuning module located near the tower base. During operation, these wires are energized with radio frequency voltage.
In this embodiment, the vertical wires are sheathed in hollow, large diameter dielectric tubes to a height of 10 feet or more. Similar tubes are used to encase the base ring and the wire to the antenna tuning module. These sheaths are then connected seamlessly at all wire junctures and exposed points such that no radio frequency voltage carrying conductor is exposed in the base area.
A further feature of this system is that the sheaths or sleeves are of much larger diameter than the wires (typically four or more times). The sleeves are loosely fitting, reducing the possibility of snagging, and are capable of rotating to release snags while still maintaining the desired dielectric properties.
An additional feature of the invention relates to the attachment of cables. In the co-location of wireless antennas on AM towers which have base insulators, it is frequently necessary to conduct grounded coaxial and other cables across the base of the tower that may be at an elevated radio frequency voltage. To accomplish the required isolation, the cables are typically formed into, or inserted within, a coil that, with its associated components is mounted within a weather-protected cabinet near the tower base.
At present, multiple cabinets of coils may be required to isolate the large number of cables encountered in installations. This gives rise to significant problems in radio frequency grounding of the cabinets, difficulties in physically siting cabinets in the limited area and proximity required, and aesthetic concerns from a jumble of cabinets.
In this invention, the isolation coils are assembled within an expandable modular architecture of compatible cellular cabinets, an example of which is shown in the attached Figure. As future demand requires, cabinets can be stacked in a manner resulting in a xe2x80x9cwallxe2x80x9d which is electrically and structurally unified. In order to accomplish this, the cabinets are fabricated in the manner of a rectangular tube with endplate inserts.
In effect, the coil with input and output fittings is slid in or out of the tube, positioned so that all output fittings are on the tower side, and all input fittings are on the side away from the tower. The four outer edges of each end of the tube are fabricated so that the attachment holes of each are exactly coincident with those of any other module.
Further, the outer attachment surfaces are of highly conductive metal, providing a high quality ground connection into the whole when attached. Also, a removable strip of similar metal is provided over these surfaces to preserve the conductivity when not in contact with another module.
Accordingly, one aspect of the present invention is to provide a broadcast tower comprising a vertical support; a plurality of vertical antenna wires having a given outer diameter spaced from the support and mounted thereon, the antenna wires having upper and lower sections and lower ends; and flexible, non-conductive insulation sleeves covering the lower section of the antenna wires, the sleeves each including an inner tubular member having an inner diameter greater than the given outer diameter of the wire and outer diameter, and an outer tubular member having an inner diameter greater than the outer diameter of the inner tubular member.
Another aspect of the present invention is to provide an electrical cable cabinet for use with a broadcast tower comprising a conductive housing having a top wall, a bottom wall, and parallel first and second side walls joining the top and bottom walls, the side walls having corresponding attachment means, whereby the first side wall of the cabinet can be aligned with and attached to the second side wall of another cabinet; a front plate; a back plate; and a non-conductive cable support frame slidable within the housing. The top and bottom walls may also have corresponding attachment means, whereby the top wall of one cabinet can be aligned with and attached to the bottom wall of another cabinet of the same construction.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment.